1. Field of the Invention
The present invention relates to a communication apparatus, a communication system, a communication program and a recording medium in which the communication program is recorded, which are utilized in a system such as a TV conference system.
2. Description of the Related Art
In a TV conference system in which a plurality of locations are connected by a communication apparatus to carry out a TV conference, in accordance with a data accumulation amount of a data buffer which is disposed in the communication apparatus, and CPU usage rate, generally carried out is a so-called flow control in which a transmission stop signal is transmitted to a communication apparatus which becomes a transmission source of data, and a data circulation amount is controlled. One example of the above system is disclosed in JP-A-7-284078. According to the flow control, since unnecessary data transfer is not carried out during a period of control, reduction of data transmission quantity, and load reduction of a communication apparatus, which comes up with it, can be provided.
In a conventional TV conference system, moving image data such as images of conference participants is transmitted from all locations to be connected. However, there are few cases that images of all locations are normally displayed in the same state, on a screen of an image display apparatus (i.e., monitor) of a communication apparatus, and for example, reception of moving image data from such a location that an image is not displayed became unnecessary data reception.
Herein, a relation between reception of moving image data and display on a monitor screen in a conventional TV conference system will be concretely described. FIG. 1 is a view which showed a display example of a monitor screen at an arbitrary location of the conventional TV conference system. In this TV conference system, it is designed in such a manner that, in a TV conference of three locations of A, B, C, when a user of a communication apparatus selects, it is possible to display images of conference participants at any one location out of two locations to be connected. In addition, it is also possible to display images of two locations in turns with a predetermined time interval, by a program of the TV conference system.
However, a communication apparatus at a location C always displays only an image of any one location, while it receives moving image data from both locations A, B. That is, reception of moving image data from the location B when images of conference participants of the location A is displayed, and reception of moving image data from the location A when images of conference participants of the location B is displayed, and so on, became unnecessary data transfer.
In addition, for example, there is such a case that another application software is activated during the TV conference, and other images than images of conference participants are displayed on a monitor screen. FIG. 2 is a view which shows a screen display example in case that word-processing software is activated during the TV conference. Since a window (display area) of the word-processing software is displayed on the foreground, a window of the TV conference system is almost completely covered up. Even in the suchlike reception of moving image data from both of the locations A, B became unnecessary data transfer.
As the number of connection locations is increased, this unnecessary data transfer is increased, and therefore, there is such a problem that lowering of transfer efficiency, delay and image quality deterioration due to excess of processing capacity of a communication apparatus, communication delay due to repetition of collisions, and so on become prominent.